The present disclosure relates to a refrigeration lubricant composition having excellent electrical insulation ability, excellent compatibility with chlorine-free hydrofluorocarbons, excellent heat resistance, and rustproof effects for rare earth magnets used in a refrigerating apparatus, and to a refrigerant working fluid composition employing such a refrigeration lubricant composition.
Conventional chlorofluorocarbon refrigerants which are used in room air conditioners, package air conditioners, low-temperature apparatuses such as refrigerator-freezers for home use, industrial refrigerators and automotive air conditioners such as hybrid cars and electric cars are being replaced because of problems, such as the ozone layer destruction. As the replacement chlorofluorocarbon refrigerants, chlorine-free hydrofluorocarbon refrigerants, such as 1,1,1,2-tetrafluoroethane (R-134a), pentafluoroethane (R-125), difluoroethane (R-32) and a mixture thereof, are known. Various refrigeration lubricants using a base stock containing a polyol type ester compound having high compatibility with chlorine-free hydrofluorocarbon refrigerants have been proposed. The properties required for the refrigeration lubricants include compatibility with chlorine-free hydrofluorocarbons, high electrical insulation ability and heat resistance. Patent Document 1 proposes a refrigeration lubricant containing a polyol type ester compound having high compatibility with chlorine-free hydrofluorocarbon refrigerants and high electrical insulation ability.
In recent years, social interest for energy conservation has been increasing, and it has been desired to reduce the power consumption of electrical products. In the case of refrigerators and air conditioners, it has been regarded as important to conserve the power of the compressor, which consumes a majority of the power of the refrigerators and air conditioners. In order to conserve the power of the compressors, a highly efficient compression mechanism has been developed, and at the same time, an increase in the efficiency of the motor in compression mechanisms has also been an important issue which would lead to power conservation of the entirety of the apparatuses.
In order to improve the efficiency of motors, more efficient and powerful magnets have been adopted for motors. For example, ferrite magnets have been positively replaced with rare earth magnets, and this contributes to a reduction in power consumption and size of electrical products. Neodymium magnets, such as Nd—Fe—B (neodymium-iron-boron), are relatively inexpensive examples of rare earth magnets. Refrigerant compressors using rare earth magnets have been proposed (see, for example, Patent Document 2). However, neodymium magnets have a low corrosion resistance and rust easily, and the magnet tends to deteriorate in quality. Deterioration of the rare earth magnets is a cause of lowering in the performance of the motor. Rust of the rare earth magnets is a cause of pipe clogging in the refrigerating cycles. Therefore, it is common to protect rare earth magnets with nickel plating or aluminum plating.
Patent Document 3 proposes a technique for protecting a rare earth magnet with a rustproof coating of sodium silicate glass instead of nickel plating in order to reduce costs. Patent Document 4 proposes a technique for protecting a rare earth magnet with a protective coating film in glass form, which is formed from a polysilazane coating film. Patent Document 5 proposes a technique for preventing rusting by carrying out heat treatment on a rare earth magnet in a low oxygen atmosphere. However, the conventional art is not suitable for motors for a refrigerant compressor which is exposed to a chlorine-free hydrofluorocarbon refrigerant or lubricant over many years. This is because under the conditions of use of the refrigerant compression motors, some components elute from the above described rustproof coating, glass-like protective coating, and heat treated film when used. This negatively affects properties of the refrigerant or the lubricant. In addition, a special technology, special equipments and special tasks are required for the manufacture of such rare earth magnets, and thus, the compressor is very disadvantageous in terms of the manufacturing costs.
Plating to a rare earth magnet lowers the magnetic flux content of the rare earth magnet. To avoid the plating process, Patent Document 6 proposes a manufacture method in which a motor having rare earth magnets is manufactured in an airtight environment with a low oxygen atmosphere. A special technology, special equipments and special tasks are also required for the technology described in Patent Document 6, and thus, the manufacture of an inexpensive compressor is difficult.
[Patent Document 1] Japanese Laid-open Patent Publication No. 5-17789
[Patent Document 2] Japanese Laid-open Patent Publication No. 11-150930
[Patent Document 3] Japanese Laid-open Patent Publication No. 2000-32715
[Patent Document 4] Japanese Laid-open Patent Publication No. 2003-17349
[Patent Document 5] Japanese Laid-open Patent Publication No. 2002-57052
[Patent Document 6] Japanese Laid-open Patent Publication No. 2003-61283